| Title | Review of the Bottle Rock Power Stretford Unit to Prepare for Future Increases in Power Plant Throughput |
|---|---|
| Authors | Kendrick, Cheri; McIntush, Kenneth E.; Mamrosh, Darryl L.; Beitler, Carrie Ann M.; Hileman, O. E. |
| Year | 2012 |
| Conference | Geothermal Resources Council Transactions |
| Keywords | Geothermal; noncondensable gas; NCG; The Geysers; H2S Abatement; Stretford; hydrogen sulfide removal; sulfur recovery; air sparger; oxidizer |
| Abstract | Bottle Rock Power (BRP) is planning to increase power plant production at its Geysers facility from 10-15 megawatts (MW) to 30 MW in the near future. The required flow rate of geothermal steam is estimated to be about 550,000 pounds per hour (lb/hr) for the planned 30 MW. The steam may contain up to 1 weight percent (wt%) of non-condensable gas (NCG) and up to 500 parts per million by weight (ppmw) of H2S. The primary H2S abatement system (i.e., the Stretford unit) will need to reliably remove H2S from the NCG to less than 10 parts per million by volume (ppmv) before the sweetened gas (composed primarily of CO2) is vented to the cooling tower. BRP contracted with Trimeric to review historic plant data to determine if the Stretford unit has ever operated under conditions similar to those expected in the future and, if not, to perform a process analysis to estimate the H2S removal possible with the existing Stretford unit at the 30 MW conditions. To prepare for the future increased loads, it is also important to improve the reliability of the BRP Stretford unit. Operating problems (e.g. plugging) cause occasional loss of the desired H2S removal efficiency. Therefore, BRP also contracted with Trimeric to review the current design and operations at the plant and suggest any needed improvements to the oxidizer and absorber systems. The current Stretford design and operations are briefly reviewed as background with important performance issues noted. Historic H2S removal rates are summarized over a range of operating conditions. The methodology used to estimate the H2S removal possible with the existing Stretford unit at the expected future 30 MW conditions is discussed. Finally, recommended improvements to key equipment areas and operations of the Stretford unit are presented. For example, in one improvement, a new air sparger was designed and installed in the oxidizers that helped produce a consistent froth that had not been observed in many years. New operating practices (such as developing protocols for exercising the plant, optimizing ADA concentration, and running at higher alkalinity and pH) were also recommended to enhance the performance and to minimize downtime of the Stretford unit. |